One of the known methods of extracting caffeine from green coffee beans is through the use of supercritical carbon dioxide. The supercritical carbon dioxide is contacted with moist green coffee beans at high pressure to extract caffeine therefrom. In these processes it is generally desirable to recirculate the supercritical carbon dioxide and, thus, it is necessary to remove the caffeine from the carbon dioxide so that it may be recirculated.
The commercial method for removing caffeine from supercritical carbon dioxide involves the use of activated carbon. Batch extraction with water is taught by U.S. Pat. No. 3,806,619 issued April 23, 1974 entitled "Process For Recovering Caffeine". Generally the extraction of caffeine from supercritical carbon dioxide must be carried out at high pressure in order to reduce the costly need to change gas pressure. Due to the cost of high pressure equipment, it is also desirable to minimize the size of the vessel used for contact of the extractant and supercritical carbon dioxide. Prior art methods employed high-efficiency packing for liquid counter current extractant of a fluid within a minimum vessel size. The packing, though efficient in contracting the two fluids can show a tendency to foul. Thus, it was often necessary to replace the packing or flush the packing in some manner to clear the fouling. This involved lengthy periods of equipment downtime and high costs. With such high pressure equipment, the necessity of changing packing is cost prohibitive.
Accordingly, there is the need in the prior art for a process and apparatus for extracting caffeine from supercritical carbon dioxide at high pressure in a manner which eliminates fouling of the extraction vessel. In addition, there is a need for a method and apparatus for high-efficiency caffeine removal from supercritical carbon dioxide which is cost-efficient and does not require long periods of downtime for cleaning.